Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several small-sized unit cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery pack having a plurality of unit cells electrically connected with each other because high output and large capacity are necessary for the medium- or large-sized devices.
As the unit cell for the medium- or large-sized battery pack is widely used a pouch-shaped secondary battery, which is generally packaged in a battery case made of a laminate sheet generally consisting of aluminum and polymer resin, and therefore, the mechanical strength of the pouch-shaped secondary battery is not high. For this reason, a plurality of unit cells are mounted in a battery cartridge, where the unit cells are connected in series and/or in parallel with each other, and a plurality of battery cartridges are electrically connected with each other to constitute a battery module.
A battery module widely used for hybrid electric vehicles has a closed-type structure in which an electrolyte cannot leak from each unit cell (secondary cell). Consequently, the closed-type battery module has an advantage of preventing leakage of the electrolyte. However, the closed-type battery module has problems in that heat generated in the unit cells is accumulated, and therefore, the accumulated heat accelerates the deterioration of the unit cells and that some of the unit cells are overheated when they are operated abnormally, and therefore, the unit cells may catch fire or explode. Lithium-ion secondary batteries or lithium-ion polymer secondary batteries, which are currently generating much interest in the potential uses of unit cells, generate heat while the secondary batteries are charged and discharged. When such heat is continuously accumulated in the unit cells, the deterioration of the unit cells is accelerated, and furthermore, the unit cells may catch fire or explode.
A battery cartridge having a novel structure to solve the above-mentioned problems and a battery module including the same have been developed by the applicant of the present application and filed with the Korean Intellectual Property Office (Korean Patent Application No. 2004-111699).
The battery cartridge and the battery module described in the above-mentioned patent application are characterized in that unit cells having low mechanical strength are stably mounted, heat dissipation from the unit cells is effectively accomplished, the overheat generated when the unit cells are operated abnormally is removed, and therefore, the service life and the safety of the unit cells are improved. Also, the battery module is manufactured in a compact structure, and therefore, it is possible to provide a small-sized but high-output, large-capacity battery module or battery pack.
On the other hand, the electrical connection between the unit cells and the coupling between the unit cells and the other components are performed in a small area so as to manufacture a compact battery module or a compact battery pack. As a result, a possibility of short circuits exists, and it is not possible to perform welding or mechanical coupling using bolts and nuts. In consideration of such difficulties, some of conventional arts proposed methods of accomplishing the electrical connection between the unit cells in a contact fashion using elastic members, such as springs. However, these conventional methods have several problems in that the mechanical strength or the resistance to vibrations is low, contact resistance is increased due to corrosion, and connected parts are easily separated from each other.
Also, the medium- or large-sized battery module or battery pack includes a plurality of unit cells, and the operating performance of the system is deteriorated due to overheating of some unit cells and high potential difference between the unit cells. For this reason, it is necessary to provide a battery management system (BMS) for monitoring and controlling the overheating of the unit cells and the potential difference between the unit cells. Consequently, an additional connecting member for connecting the unit cells and the BMS is needed. However, the use of a large amount of components in a compact battery module or battery pack may cause the above-described problems.